The present invention relates generally to an imaging reader for, and a method of, electro-optically reading targets by image capture, and, more particularly, to a color image processing pipeline for processing color images of the targets captured by a solid-state color image sensor in the reader for either storing or displaying at least one of the targets, e.g., a non-symbol target, with high fidelity, or for decoding symbol targets without degrading reader performance.
Solid-state imaging systems or imaging readers have been used, in both handheld and/or hands-free modes of operation, to electro-optically read targets, such as one- and two-dimensional bar code symbols, and/or non-symbols, such as documents, drivers' licenses, receipts, damaged products, and like objects, people, places, or things, over a range of working distances relative to each reader. Each reader generally includes an imaging assembly having a solid-state imager or imaging sensor with an array of photocells or pixels, which correspond to image elements or pixels in an imaging field of view of the imager, and an imaging lens assembly for capturing return light scattered and/or reflected from the target being imaged, and for projecting the return light onto the imager to initiate capture of an image of each target. The imager may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device, and associated circuits for producing and processing electrical signals corresponding to a one- or two-dimensional array of output raw image data over the imaging field of view.
Many readers use monochrome imagers, which produce monochrome or gray scale images that are well suited for reading and decoding symbol targets. However, when the readers are also tasked with displaying targets, such as non-symbol targets, monochrome imagers have not proven to be that well suited for displaying non-symbol targets. Many users prefer to view images of non-symbol targets in color. In some cases, the color images may actually be clearer, or more informative, than the monochrome images. As a result, color imagers, which are typically overlaid and integrated with color filter arrays, such as Bayer filters, are becoming more prevalent in such readers that can read both symbol and non-symbol targets.
In order to display a target with high color fidelity, each such color imager employs a color image processing pipeline to process the output raw image data from the color imager. The pipeline is a set of components or processing blocks that are situated between the color imager and a display, such as a monitor or screen. Such pipeline components may typically include such components as a white balance component for adjusting pixel luminance among bands of red (R), blue (B) and green (G) colors in the output raw image data, a de-mosaic component for processing the output raw image data from the imager to reconstruct the captured color image, a pixel transform component for adjusting a bit depth of the output raw image data, a color correction component for applying a blending matrix to convert an RGB color space from the color imager to a different standard color space, a gamma correction component for adjusting image quality to add, remove, or modify nonlinearities in the output raw image data, a noise filter component for removing noise from the output raw image data, and an encoding component for converting between color image formats in the output raw image data.
Although the color image processing pipeline is generally satisfactory for its intended purpose of displaying a color image of a target with high fidelity, one or more of the pipeline components can sometimes degrade reader performance when the reader is decoding a symbol target. More particularly, the color correction component and/or the gamma correction component and/or the noise filter component can generate excess noise, and can, at least partially, and sometimes significantly, reduce the working distance range. This is unacceptable, especially in a venue that requires the targets to be read over an extended working distance range.
Accordingly, there is a need not to degrade reading performance in the decode mode in such readers having color imagers that can image and read both symbol and non-symbol targets.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The pipeline, reader, and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.